Modern households continue to use increasing amounts of electronic hardware in an effort to promote a higher standard of living. Many electronic devices such as televisions, stereos, VCR players, alarm systems, children's toys and so on use remote-controlled signaling devices in their operation. The result of these electronic devices is an increasingly noisy environment throughout the commonly used remote-control signal frequencies.
One way to prevent interference in remote-control signals is to create narrow-band systems in which each individual device uses a distinct band of frequencies. In theory, if each device used a distinct band of frequencies, no interferences would occur. However, we do not live in a perfect world. Many unrelated remote-controlled devices have overlapping control frequencies. Additionally, random signals produced by such items as fluorescent light bulbs or a neighbor's remote-control transmitter, inevitably cause intermittent interference signals. Consequently, narrow band remote-control devices have inherent disadvantages that adversely affect their operational effectiveness.
The present invention uses spread-spectrum technology to create a remote-control link. Spread-spectrum devices do not use a narrow band. Consequently, spectrum devices are less sensitive to fixed-frequency interference signals or noise signals with emphasized frequency ranges. Additionally, spread-spectrum devices work efficiently when the transmitter energy is low and the frequency of the signal to be transmitted is low, compared with the data rate of the spread-spectrum signal. This characteristic makes spread-spectrum systems even more desirable for household uses because household devices utilize hand-held, low power, low frequency transmitters.
Spread-spectrum technology is not new. The use of spread-spectrum receivers are exemplified in U.S. Pat. No. 4,875,221 to Mori and U.S. Pat. No. 4,774,715 to Messenger. Remote-control systems, utilizing spread-spectrum receivers and transmitters, are exemplified by EP 360,476 to Carlin and EP 131,458 to Diederich.
See also a text entitled "Spread Spectrum Systems" by Robert C. Dixon published by John Wiley & Sons, Inc. (1984). This text gives examples of spread spectrum systems as well as the mathematics and operation of said systems.
The present invention utilizes spread-spectrum technology to create a remote-control system whose control commands are dictated by the relative position between the receiver and the transmitter. Such position controlled spread-spectrum technology is addressed in EP 377,055 to Heberle. However, the prior art has certain disadvantages. Position controlled spread-spectrum transmitters transmit multiple continuous-wave signals. The transmission is a great drain on the battery source of a hand-held transmitter, resulting in short battery life.
The present invention improves upon the prior art creating a position controlled, remote-control system whose electrooptical transmission link is immune to interference. The apparatus uses a low transmitting power and is particularly well suited for hand-held transmitter applications.
It is therefore a principal object of the invention to provide an improved electrooptical transmission link for position controlled, remote-control systems.
It is a particular object to create an electrooptical transmission link that is immune to interference, has low maximum transmitting power and is well suited for hand-held transmitters.